1. Field Of The Invention
This invention is in the field of cutting tools and processes for making a thread in or on a workpiece. More particularly, this invention relates to combined hole making, threading, and chamfering tools for making a hole, a thread, and/or a thread in a workpiece.
2. The Prior Art
The prior art has employed various tool structures for cutting holes, threads, and/or chamfers in a workpiece. Application and performance specifications of cutting tools influence manufacturing designs and processes, such as in the high speed machining art. Problems with prior art cutting tool structures include limitations of their use and/or inconsistent performance in the manufacturing process. For example, cutting conditions can cause the cutting tool to break, to diminish its performance, to deflect and produce poor results, and/or to cause cutting edges to lose their effectiveness due to increased wear.
U.S. Pat. No. 4,761,844, incorporated herein by reference, relates to a combined hole making and threading tool for drilling a hole in a workpiece on the inward feed of the tool and for threading the hole. The tool comprises a straight body with a hole making means such as a drill point or center cutting end mill feature at the forward end, a shank at the rearward end, and a thread form mill between the hole making means and the shank. U.S. Pat. No. 5,429,459, also incorporated herein by reference, relates to a method of and apparatus for thread mill drilling.
FIG. 1 is a prior art combined hole making and threading tool, generally illustrated as 100, having a shank 102 at one end, a drill point 104 at the forward end, and a thread-form mill 108 intermediate the drill point 104 and the shank 102. The thread-form mill 108 is provided with a multiplicity of thread-form cutters 112 and one or more flutes 110 extending from the drill point 104 throughout the thread-form mill 108 for the purpose of chip removal. Each thread-form cutter 112 comprises a number of cutter segments 114a and 114b circumferentially aligned and separated by the intervening flute 110. Each of the thread-form cutters 112 is of annular configuration. The number of thread-form cutters 112 is preferably equal to or greater than the number of threads to be cut. During a thread cutting phase, the thread cutting segments 114a and 114b are laterally displaced into the wall of the hole. As the tool rotates, threads (not shown) are cut in the wall of the hole in the workpiece, generating cutting forces that act on the tool 100, including the thread-form mill 108.
The resulting thread-cutting forces can result in deflection in the tool, thus diminishing the thread tolerance. Under certain applications, such forces can limit the feed rate at which the tool can operate, and increase the thread cutting time, and/or cause the tool to break. What is needed is a cutting tool design that will overcome such prior art problems.
Although certain prior art thread cutting tools may have incorporated flat thread cutting inserts, such tools have limited applications. For example, prior art thread cutting inserts are flat, do not have helical angles, and suffer from the disadvantages of convention (non-staggered) thread cutting edges. Furthermore, such thread cutting inserts are not suitable for hole making cutting edges or chamfering cutting edges. Also, prior art flat thread cutting inserts are not suitable for use with combined hole making, threading, and chamfering tools, particularly combination tools with helical thread cutting teeth.
Another problem with prior art thread cutting tools and combined hole making, threading and chamfering tools concerns the wear of the cutting edges, manufacturing of such tools, and replacement costs. For example, such tools are manufactured from carbide and require precise grinding to form the hole making, threading, and/or chamfering cutting edges. After the cutting edges have excessive wear, the entire carbide tool must be replaced, and it is typically necessary to grind another carbide tool with the desired cutting geometries. Replacement of the entire cutting tool for wear on a small portion of the tool substantially increases associated operating costs.